THERMORCHEMISTRY

FIRST TIPS TO MASTER IN THIS TOPIC:

1. You need to have a calculator.
2. Good in conversion of mol to mass, mol to no. of particles, mol to volume of gas in room condition and STP.
3. Balance the equation.
4. Label the unit with the respective symbols.

 WHAT YOU NEED TO KNOW FROM THIS TOPIC:

1. Differentiate between the bond breaks and the bond reforms.
2. If the reactants breaks a bond = the heat is absorbed.
3. If the product reforms ( forming a bond ) = the heat is released.
4. When the total energy absorbed is more than the total energy released = Endothermic reaction.( with a positive sign, + ).
5. When the total energy absorbed is less than the total energy released = Exothermic reaction. ( with a negative sign, - )
6. List the examples of the endothermic reactions and exothermic reaction. Make sure you enable to write the equation correctly and state the observation.
7. Enable to describe the endothermic reaction / exothermic reaction.

For example:

 CH₄ + 2O₂ à CO₂ + 2H₂O     ΔH = -890 kJ mol^-1

a)     The combustion of methane is exothermic reaction.

b)     1 mol of methane burns completely in excess oxygen to form 1 mol of carbon dioxide gas and 2 mol of water releases 890kJ heat energy.

c)      The total energy absorbed when methane breaks the bond is lower than the total energy released when carbon dioxide and water were formed.

d)     The surrounding temperature is rise.

8. Draw the energy level diagram. ( EXXO =  Z, energy content in reactants is higher , ENDO = S, energy content in reactants is lower. )

    9. EXOTHERMIC AND ENDOTHERMIC REACTION IN DAILY LIFE

 a)     coal is burnt heat is given off. The heat given off is used for cooking or to keep the house warm

b)     Cold packs and Hot packs are often used in sports. They are used to lessen pain for injuries. Salts used in cold packs – NH₄Cl , NH₄NO₃, Na₂S₂O₃, KNO₃ packed separately with water. Salts used in hot packs – AlCl₃, CaO₃ , CaCl_.2H₂O, CuSO₄.2H₂O used to dissolves in water. When the pack is needed, the membrane is broken.

    10. TO CALCULATE THE ENERGY CHANGE:

                                       ΔH = mcθ

m = the mass of water used in the reaction(for combustion, water is used to  

       absorbed the heat release from the burning of ethanol).

c = the water heat capacity , 4.2 Jg^-1oC^-1

θ = the changes in the temperature of water used.

Chapter 3. F4: Chemical Formulae and Equations

1. Relative atomic mass and mole of atoms.
a. 1 mole of an element has a mass (in grams)  that is equal to its relative atomic mass.

Atom	Relative atomic mass	Mass of 1 mole (g)
Hydrogen, H	1	1
Carbon, C	12	12
Oxygen,O	16	16
Sodium, Na	23	23

  b. RAM has no unit because it's only a ratio.
 c. if more than 1 isotopes of the element is present, the RAM is calculated by an average of both isotopes's RAM.
d. Why Carbon-12 is used as a standard.
  - its mass is aesily measure with mass spectrometer
  - easily found as its compounds are abundant.
2. Relative molecular mass, RMM
a. A molecule is made up of tho or more atoms. If we know the RAM of all atoms in a molecule, we can calculate the RMM .
b.

Molecule	Molecular formula	Relative molecular mass
Chlorine gas	Cl2	2 x 35.5 = 72
Nitrogen gas	N2	2 x 14 = 28
Ammonia	NH3	14 + ( 3 x 1 ) = 17
Ethanol	C2H5OH	(2 x 12) + (6) + 16 = 46

3.The Mole
 a. the amount of substance is measure by unit of mole
b. the symbol of mole is mol.
c. by using the mole we can calculate the
    - number of particles,  ( x N_A).
    - mass of substance , ( x RAM@RMM )
    - Volume of Gas, ( x 22.4dm-3 - STP and x 24 dm-3 at room condition )
4. Chemical Formulae
a. Symbols are used in chemical formula.
b. The formula of molecules tells us -
    -  the name of a substance
    -  the number of atoms of each element present
c.

Compound	Formula	Information
Nitrogen gas	N2	2 atoms of Nitrogen atom in 1 molecule
Hydrogen chloride	HCl	1 atom of hydrogen and 1 atom of Chlorine in 1 molecule of hydrogen chloride
Ammonia	NH3	1 atom of nitrogen and 3 atoms of hydrogen in 1 molecule of ammonia
Sulphuric acid	H2SO4	1 molecule of sulphuric acid contains 2 atoms of hydrogen, 1 atom of Sulphur and 4 atoms of oxygen

5. Empirical Formula and Molecular Formula
 a. Empirical formula only show the simplest ration of elements in it. ( not the actual formula ).
b. Molecular formula shows the actual number of each type of element in it.
c. to determine the empirical formula of MgO
.  - the crucible with its lid are weighed.
  - the crucible together with the lid and Mg ribbon are weighed.
- heated the crucible strongly without lid.
 - when Mg start to burn cover the lid.
 - the crucible's lid is lifted from time to time until the Mg stops burning.
 - the lid is removed and heated strongly for 2 minutes.
 - let the crucible cool down to room temperature and weighed again with the lid.
 - repeat the process of heating , cooling and weighing until a constant mas is obtained.
Observation:
 - metal Mg turns to white solid.
- Precaution measures that's very important to remember:
- sand paper is used to remove the oxide layer
 - the crucible's lid is removed from time to time to allow oxygen enter and oxidised the Mg ribbon.The Lid is then replace quickly to prevent fumes of MgO from escaping.
 - the heating, cooling and weighing process are repeated until a constant mass is obtained.
 - this method also can be used to determine the empirical formulae of reactive metals such as aluminium oxide and zinc oxide.
 d. empirical formula for Copper (ii) oxide ( CuO )
 - fill in 1 spatula of CuO in porcelain boat and weighed then put in the combustion tube.
 - allow dry H₂ gas to pass through the combustion tube for a few second, the excess H₂ gas is ignites at the other end of combustion tube.
 - the CuO is heated strongly for 10 minutes and let the dry H₂ gas to pass through the combustion tube until it cool to room temperature.
- the mass of porcelain boat with Cu is weighed again.
- observation :
 - black colour of CuO turns to brown Cu.
 - Precaution Measures :
 - Dry hydrogen gas is pass through in the beginning of experiment is to remove all the air in the combustion tube.
 - the excess hydrogen gas is ignites is to confirm that all the air is removed. ( if the ignite gas burn without a "pop" sound means that all air is removed ).
 - the hydrogen gas is continuously pass through when the combustion tube is set to cool because to prevent the hot Cu react with Oxygen gas to form CuO again.
- heating cooling and weighing are repeated until a constant mass is obtained.
 -this method also can be used to determine the impirical formula of less reactive metals such as lead(II) oxide and tin(II) oxide.
 6. Molecular Formula
a. shows the actual number of atoms of each element that are present in a molecule of the compound.

       Molecular Formula = ( empirical formula )_n where n is a integer.

b. Add all the RAM present , times n = Mass of molecule,
 got the n, then replace in the formula.
7. Percentage Composition by Mass of an element in a compound
 
% composition by   = Total RAM of the element in compound
 mass of element                        RMM of compound

Try to write the chemical formulae and names of the following common compounds.

Exhibition on the science projects

Dear Jambulian,
There will be an exhibition on the science project by form 2, 3 ,4.and 5 on 28- 31st of March 2011.
The task is conducted by group of 6. What you need to do is just get a form from your science teacher and choose the concept that you are going to show.
Your science teacher will become your advisor. The exhibition is based on proving and showing how a science concept is being applied to the daily activities.
Choose a topic, find the best activity to show, know the learning objectives, prepare a script, then plan for a show. That's it.
So what are you waiting for, just grab a chance!!! Win the prize..... and... 
Be a magician..... Zaaaazzzzzz......

THE 5 MODELS OF ATOM

Chemistry is the study of matter and the changes that it undergoes. Since all matter consists of atoms, it is important that you understand the atom and its components especially the electron.

Why the electron? Because the electron configuration determines how an element will behave in chemical bonding and chemical reactions. So if you understand the electron you will better understand chemistry.

Although models are not perfect there are five models of the atom that lead to the understanding of matter. The more you understand these models the better you will be at chemistry. The five models are:
The Solid Sphere model
The Plum Pudding Model
The Nuclear Model
The Bohr Model
The Wave Mechanical Model

Solid Sphere Model
The solid sphere model was proposed in 1803 by John Dalton. John Dalton was an English chemistry and math tutor who took the ideas of his day and put them into a model of how matter was arranged. He stated that matter was made of tiny indivisible particles called atoms and atoms of the same element were all alike. Also, he included the law of multiple proportions and the law of definite composition in his model. Although his model was not perfect it was the main main model for over 90 years.
Plum Pudding
In 1897 English physicist, J. J. Thomson, suggested that cathode rays consisted of negatively charged particles even smaller than atoms. As a matter of fact he suggested these particles were subatomic parts of the atom. Thus, Dalton’s theory of an indivisible particle was no longer workable. A new theory that allowed for subatomic particles was needed.
So, Thomson proposed that the atom was a mass of positive charge with negative electrons placed into it like raisins in a pudding, and dubbed it the Plum Pudding model. Thomson’s model, although attractive, nevertheless had many shortcomings.
The Nuclear Model
In 1906 Ernest Rutherford and his assistants, performed the famous Gold Foil experiment that led to the discoveries of the atomic nucleus and that the atom is mostly space.
The Gold Foil experiment demonstrated that the mass of the atom was the same as predicted by Thompson’s model, but the volume of the mass was much smaller and seemed to be located in the center of the atom. Thomson’s Plum Pudding model was no longer workable. So, in 1911, Rutherford proposed the Nuclear model of the atom.
The Bohr Model
In 1913 Danish physicist, Neils Bohr, suggested applying the quantum theory to the Rutherford model. Bohr’s new model proposed that electrons are in fixed energy levels he called orbits. The energy of these orbits is quantized and electrons must absorb or release energy (photons) at certain wavelengths to move between energy levels.
The Wave Mechanical Model
In 1921 Louis de Broglie stated, without any empirical evidence, that if waves have matter properties then matter should have wave properties. Later, Bell Laboratories would prove that De Broglie’s hypothesis was indeed correct. De Broglie’s hypothesis was a revelation that even impressed Einstein and changed the view of the atom forever.
Combining Louis de Broglie’s hypothesis with Bohr’s model, Erwin Schrodinger proposed the electron was a 3-D waveform circling the nucleus in a whole number of wavelengths allowing the waveform to repeat itself as a stable standing wave representing the energy levels of the Bohr model.
In support of his hypothesis, Schrödinger developed a mathematical equation to describe the wave-like behavior of the electron. The Schrödinger wave equation not only gave the correct energy levels for the hydrogen atom, but also was somewhat useful in atoms with more than one electron. This mathematical description of the details of atomic behavior became known as the “Wave Mechanical Model”.
Chemistry – The Atomic Models and Chemistry

The Structure of the Atom - Chapter 2 F4

1. Matter is anyting that occupy space and has mass.
2. Definitions:
 - Atom - is the smallest particle of an element that can participate in a chemical reaction, tiny and discrete( isolate from one and another)
 - Molecule - is a group of two or more atoms which are chemically bonded together.( covalent / ionic bond )
 - Ion - positively charge / negatively charged particle, ( atom that losing electron > +ve ion / atom that receive electron > -ve ion )
3.  The kinetic theory of matter - discuss the arrangement and moving of particles, the forces of sttraction between particles and the energy content in the particles in the different state of matter.
4. The change in the state of matter is caused by heat supply to the particles.

----------------------------------------------------->
the increasing of heat : turn the solid particle to liquid and to solid

<-----------------------------------------------------
the decreasing of heat: turn the gas particle to liquid and to solid

the heat supply is absorbed by the particle. it cause the particle to move ( vibrate ) faster and overcome the force of attraction between the particles at their fixed positions.. the point where the solid particles become liquid is called "melting point" at this point the temperature is remains constant .

when the heat is released to the surrounding by the particles, ( the cooling process ) it cause the particle to lose their kinetic energy so, it moves slower. The particles then closer and attract to each other to form solid. At the point where the liquid becomes solid is called " freezing point". At this point the temperature remains constant.
5. The atomic structure=
a) John Dalton - a very tiny ball.
b) JJ Thompson- plum pudding model - atom is a sphere +vely charged with -vely charged particles called electron surround it.
c) Ernest Rutherford - atom have a +vely charge at the central region called nucleus with -vely charged particles electron moves around it.
d) Neils Bohr - electron moves in an orbit called shell.
e) James Chadwick - neutron gives half of the mass of atom and exist in the nucleus.
6. Subatomic particles of an atom=
a) Proton - relative electric charge = +1, relative mass 1
b) Neutron - relative electric charge = 0, relative mass 1
c) Electron - relative electric charge = -1, relative  mass 0.0005
7. Proton + Neutron = Nucleon , in nucleus of atom
8. Definitions =
 a) Proton number = is the number of protons in its atom
 b) Nucleon number =  is the total number of protons and neutrons in its atom.
9. the different proton number shows the different element. refer to the periodic table and make sure you enable to write the symbol of the element and their respective proton number and nucleon number.
10. the atom of the same element with different neutron number is called isotopes. examples are ; for Oxygen, O-16,O-17, O-18, or for Carbon, C-12, C-13, C-14.

11. Isotopes

1. Isotopes are atom of the same element with same number of proton but different number of neutrons.
2. Isotopes are atoms of the same element with same proton number but in different nucleon number.
3. Example :

1   H 1	2   H 1
Nucleon number = 1	Nucleon number = 2
Proton number = 1	Proton number = 1
Number of neutron = 0	Number of neutron = 1
-         Hydrogen -1 and hydrogen-2 are isotopes . Both have the same number or the same number of protons but in different in nucleon number because of the difference in the number of neutrons. -         Isotopes have the same chemical properties but different physical properties because they have the same electrons arrangements.

4. Uses of isotopes

i-                    Medical field          

-           To detect brain cancer

-           To detect thrombosis ( blockage in blood vessel ).

-           Sodium-24 is used to measure the rate of iodine absorption by   

            thyroid gland.

                  -           Cobalt-60 is used to destroy cancer cells.

                  -           To kill microorganism in the sterilizing process

ii-                  In the industrial field

-                     To detect wearing out in machines

-                     To detect any blockage in water, gas or oil pipes.

-                     To detect any leakage of pipes underground

-                     To detect defect/ cracks in the body of an aeroplane

iii-                 In the agriculture field

-                     To detect the rate of absorption of phosphate fertilizer in plants

-                     To sterile insect pests for plants.

iv-                In the archeology field

-           Carbon-14 can be used to estimate the age of artifacts.

12. Electron arrangement

1. the electrons are filled in specific shells. Every shell can be filled only with a certain number of electrons. For the elements with atomic numbers 1-20 ;

-         First shell can occupy with a maximum of 2 electrons.

-         Second shell can occupy with a maximum of 8 electrons.

-         Third shell can occupy with a maximum of 8 electrons.

b. Valence electrons are the electrons in the outermost shell of an atom.

Rate of reaction - Form 5

 1. Rate of reaction -   the changes occur / time taken for the changes to happen.
 2. There are 2 type of ROR-
      - average ROR - the total time taken for changes measured.
      - instantaneous ROR - the changes take place at a given time
 3. To calculate the average ROR is by measure the total changes occur and divide by the total time taken
     until the reaction is stopped.
     Example: The reaction of zink with hydrochloric acid-
                    a) the volume of hydrogen gas given off = 35.0 cm3.
                    b) the total time for reaction to stopped = 210 s
     So, the Average ROR = 35.0 / 210 = 0.17 cm3/s
  4. To calculate the instantaneous ROR -
      - you a need a graph of the reactant deacreases / product increases( Y axis) against the time ( X axis).
      - use a ruler to draw a tangen close to the point on the graph at given time.
        ( if the reactant decreases graph- make sure the tangen is not over/cross the curve of your graph )
        ( if the product increases graph - make sure the tangen is on top of the curve and not crossing the curve)
       - from the tangen draw a triangle and find the lengh of Y axis for the trianle  = dY, and
         and find the lenght of X axis for the trangle = dX
       - the Instanteneaous ROR  is  dY / dX.
       - tips - make sure the graph is evently scaled and the curve is smooth.
 5. Operation definition for Rate of  Reaction ( ROR) -
       - To measure the time taken for changes to occur ( the responding variable )  by using 
          stopwatch.
       - the responding variable could be the volume of gas liberated, decreases of reactant mass, increases
          of  product mass or the increases or decreases of temperature.
 4. There are 5 factors that affect the ROR-
       a) size of reactant - the bigger the size, the smaller the expose surface area.  so, the less number
           of collision to occur. Therefor the lower frequency of collision and the lower rate of reaction.
          - the smaller the size of reactant, the larger total surface area. So, the more collision to occur.
            Therefor the higher frequency of collision, effective collision and the higher rate of reaction.
          - Example of experiment - 20g of calcium carbonate chips and 20g of calsium                            
            carbonate powder with  25 cm3 of 0.5 moldm-3 Hydrochloric acid. The total rate of  reaction is
            calculated by measure the volume of Hydogen gas released per time taken. The apparatus needed
            are burette, basin, stopper with deliver tube, conical flask, measuring cylinder ,retort stand and stop
            watch.
       b) concentration of reactant -
          - when concentration of reactant is high, the more reactant can collide and more effective 
            collision occur. Therefor the ror is high.
          - when concentration of reactant is low, the less reactant can collide. Therefor the ror is low.
          - Example of experiment - 45cm3 of 0.5 moldm-3 sodium thiosulphate with  5 cm3 of 0.5 moldm-3
             Hydrochloric acid. The total rate of  reaction is calculated by measure the time taken of marked (on
             a white paper )dissappear.the experiment is repeated with different volume of Sodium thiosulphate in
             the solution. The apparatus needed are conical flask, measuring cylinder, filter paper, white paper
             with marked and stopwatch.

       c) temperature of solution -
         - when the temperature of solution is high , the particles of reactants have more kinetic 
            energy and it moves faster. Therefor more effective collision take place. So,the ROR is high.
         - cooling a mixture will slow down theparticles of reactants. so, fewer collisions take place and ROR is
           low.
        - Example of experiment - 45cm3 of 0.5 moldm-3 sodium thiosulphate with  5 cm3 of 0.5 moldm-3
           Hydrochloric acid. The total rate of  reaction is calculated by measure the time taken of marked (on a
           white paper )dissappear.The experiment is repeated with different temperature of Sodium thiosulphate
           solution. The apparatus needed are conical flask, measuring cylinder, filter paper, white paper with
           marked,thermometer and stop watch.

      d) Pressure on reactants -
         - the higher pressure will decrease the volume of reactants. Therefor the                         
           distance between particles is small.( the reactant is closer ). So, more effective                                 
           collisions will take place and the ROR is higher.                              
       e) Catalyst on reaction -
        - all reactions require energy . the reaction only occur if the reactants achieved the energy level. The
          energy needed is called Activation Energy, Ea. The reaction only can happen if the reactants achieve at
          least (or more) than Ea.
       - the presence of catalyst will lowered the energy level. Therefor the reaction                              
          takes place faster because more reactants are easier to collide and react.
      -  Example of experiment - The decomposition of Hydrogen peroxide 20 - volume. The total rate of 
          reaction is calculated by measure the time taken of glowing splinter to ignite.The experiment is
          repeated with the presence of Manganese (iv)oxide as catalst. The apparatus needed are conical flask,
          measuring cylinder, glowing splinter and stop watch.
       - application of catalyst in industry and daily life:
          i ) Combustion of charcoal - smaller sizes in burning with oxygen.
         ii ) Storing food in refrigerator - cold place to keep food stay fresh longer
            - to lower the activiteis of bacteria
         iii) Cooking food in Pressure Cooker - the higher pressure will increase the cooking temperature and
              the food is cooked faster.
        iv ) Haber Process - presence of iron powder as catalyst. The magnufacture of ammonia is faster.
        v  ) Contact Process - presence of Vanadium (v) oxide as catalyst, at 500C and pressure of 2 to 3 
              atmosphere.The magnufacturer of Sulphuric acid.
        vi ) Ostwald Process - Combination of Platinum and Rhodium as catalyst in 850C and pressure of 5
              amp. The magnufacturer of Nitric acid.

                                                                                                                              ZAL F5-Jan2011

welcome.

Salam,
For the year 2011, my dream is to convince all my student that they can achieve their dreams, by sharing the ideas. All of us have given a gift to be creative and these gifts is to give. By sharing ideas we can strive for excellent. By using the gift, we can together stand different from others.
So, dont work too hard to get an A, but work smart to hold the A.
Come!!!  rise with me, in this jurney to achieve our dream.
Lets, start...